Dirigent isoflavene-forming PsPTS2: 3D structure, stereochemical, and kinetic characterization comparison with pterocarpan-forming PsPTS1 homolog in pea
Bibliographic record
Abstract
Pea phytoalexins (–)-maackiain and (+)-pisatin have opposite C6a/C11a configurations, but biosynthetically how this occurs is unknown. Pea dirigent-protein (DP) PsPTS2 generates 7,2ʹ-dihydroxy-4ʹ,5ʹ-methylenedioxyisoflav-3-ene (DMDIF), and stereoselectivity towards four possible 7,2ʹ-dihydroxy-4ʹ,5ʹ-methylenedioxyisoflavan-4-ol (DMDI) stereoisomers was investigated. Stereoisomer configurations were determined using NMR spectroscopy, electronic circular dichroism, and molecular orbital analyses. PsPTS2 efficiently converted cis -(3 R, 4 R )-DMDI into DMDIF 20-fold faster than the trans -(3 R ,4 S )-isomer. The 4 R -configured substrate's near β-axial OH orientation significantly enhanced its leaving group abilities in generating A-ring mono-quinone methide (QM), whereas 4 S -isomer's α-equatorial-OH was a poorer leaving group. Docking simulations indicated that the 4 R -configured β-axial OH was closest to Asp 51 , whereas 4 S -isomer's α-equatorial OH was further away. Neither cis -(3 S ,4 S )- nor trans -(3 S ,4 R )-DMDIs were substrates, even with the former having C3/C4 stereochemistry as in (+)-pisatin. PsPTS2 used cis -(3 R, 4 R )-7,2′-dihydroxy-4′-methoxyisoflavan-4-ol [ cis -(3 R, 4 R )-DMI] and C3/C4 stereoisomers to give 2ʹ,7-dihydroxy-4ʹ-methoxyisoflav-3-ene (DMIF). DP homologs may exist in licorice ( Glycyrrhiza pallidiflora ) and tree legume Bolusanthus speciosus, as DMIF occurs in both species. PsPTS1 utilized cis -(3 R, 4 R )-DMDI to give (–)-maackiain 2200-fold more efficiently than with cis -(3 R ,4 R )-DMI. PsPTS1 also slowly converted trans -(3 S ,4 R )-DMDI into (+)-maackiain, reflecting the better 4 R configured OH leaving group. PsPTS2 and PsPTS1 provisionally provide the means to enable differing C6a and C11a configurations in (+)-pisatin and (–)-maackiain, via identical DP-engendered mono-QM bound intermediate generation, which PsPTS2 either re-aromatizes to give DMDIF or PsPTS1 intramolecularly cyclizes to afford (–)-maackiain. Substrate docking simulations using PsPTS2 and PsPTS1 indicate cis -(3 R, 4 R )-DMDI binds in the anti -configuration in PsPTS2 to afford DMDIF, and the syn -configuration in PsPTS1 to give maackiain.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".